Zinc oil additives

I use Castrol 10w40 in my 318 with a bottle of STP that has zinc in it in my73 valiant with a Purolator filter my dad used to use it in his satellite back in the70s , never had any problems. when I used 15w40 in my 318 duster I had to drain it out the lifters were going tapity tapity tap tap.. I went back to 10w40 Castrol with STP.